The formation of metal members by stretch forming to the yield point over a conforming mold is well known. Such techniques involve a certain amount of spring back which is difficult to account for in the design of the mold over which the member is stretched.
In the manufacture of a precision surface such as the parabolic shape usually required for the reflector used in microwave antennas, the accuracy with which a sheet of reflective material such as aluminum can be maintained relative to a precise mathematical paraboloid surface is a factor which affects the overall performance of an antenna in which the reflector is used. Such reflectors are now commonly used in microwave antennas known as horn reflector antennas which have apertures of 6 feet in diameter or larger. Since the reflector sheet is generally positioned at approximately 45.degree. to the axis of the antenna aperture, the area of the actual reflector is much larger than the horn antenna aperture.
In horn reflector antennas, the actual portion of the paraboloid surface which is used as a reflector depends on design parameters which dictate which portion of the total paraboloid is required to be produced as a reflector with an effective area for each particular antenna design. Once such a design is fixed, the mathematical definition and location of the paraboloid surface are readily ascertained but the formation of an aluminum sheet to assume and maintain that mathematically precise locus is only accomplished with difficulty. Typical manufacturing errors for a 10 foot aperture horn reflector antenna are approximately 0.020 inches rms.